Drilling weight control system



Sept. 4, 1951 A. G. H. STRAATMAN DRILLING WEIGHT CONTROL SYSTEM FiledApril 12, 1950 HIS ATTORNEY Patented Sept. 4, 1951 DRILLING WEIGHTCONTROL SYSTEM Alphons G. H. Straatman, The Hague, Netherlands, assignorto Shell Development Company, San Francisco, Calif., a corporation ofDelaware Application April 12, 1950, Serial No. 155,387

In the Netherlands April 21, 1949 Claims. (Cl. 254-473) The presentinvention relates to well drilling control systems by which the drillbit fed into the formation being drilled is controlled in accordancewith the weight supported on the bit, and pertains, more particularly,to an improvement over the control apparatus of the type described inUnited States Patent No. 2,371,953, issued March 20, 1945, to Crake.

During the drilling of a borehole, part of the total weight of a stringof well drilling tools is taken up by the bit resting on the bottom ofthe borehole, while the remainder of said weight is taken up by ahoisting cable through the traveling block from which the drilling toolsare suspended. In order to keep the bit pressure constant during thedrilling operation, efforts are exerted to maintain the tension on thecable as far as possible constant during drilling by controllingrotation speed of the hoisting drum on which the working part of thecable is wound. Since considerable demands are made on both the staminaand attention of the drilling crew in keeping the cable tension constantwhen a manually-operated brake drum is employed, devices forautomatically controlling the feed of cable forming a hoisting drum havebeen designed.

The United States Patent No. 2,371,953, to Crake, for instance,discloses a device whereby the weight of the drilling tools is utilizedto drive a pump, and the discharge pressure generated by the pump ismaintained at a value corresponding to the required pressure of the biton the bottom of the borehole. To accomplish this effect, the pump iscoupled to the hoisting drum of the drilling installation.

Since the feeding of the drill bit generally proceeds with slight jerksresulting from the hoisting drum stopping from time to time, it will beseen that the frictional resistances in the hoisting system varyconsiderably depending upon whether the system is in motion or at rest.Thus, the frictional resistances existing when the hoisting drum isstarted from its stationary position are greater than those occurringduring the continuous movement of the drum and its associated parts.Consequently, the whole mechanism is not set in motion again until thatpart of the weight of the drilling tools which is taken up by the cablein the hoisting drum has been increased beyond its predeterminedconstant value and the pressure on the bit! has, therefore, been reducedto the same extent. Thus, it may be seen that a substantially constantbit pressure is not maintained for any period of time by devices of thistype.

The present invention is broadly based on the principle that in order tomaintain the required constant bit pressure when the hoisting drum andits associated parts are set in motion, it is essential to lowerslightly the pressure which the pump must generate until motion isstarted, whereupon this pressure is once more raised to the value atwhich it is normally maintained.

According to the present invention, the pressure which the pumpgenerates is, therefore, periodically reduced for a short interval,irrespective of the feeding device being at rest or in motion. Theduration of this decrease in pressure is so short that it has no effecton the bit pressure to be normally maintained, but is, nevertheless,sumciently long when the feeding device is at rest to deliver acompensation for the frictional resistances occurring at that time.

It is, therefore, an object of this invention to provide a controlsystem for automatically maintaining a constant pressure or weight onthe drill bit, irrespective of the frictional resistances in thehoisting system. The present automatic control system in eliminatingvariations in pressure caused by the frictional resistances of thehoisting system, increases the bit life and gives a faster rate ofpenetration of the drill bit into the formation, due to the increasedpercentage of total drilling time during which the drill bit is engagingthe earth formation at the optimum pressure. The present automaticcontrol system likewise yields straighter and better gauge boreholes.

With the above and other objects and advantages in view, the inventionhas particular relation to certain novel features of construction,operation, and arrangement of parts, an example of which is given inthis specification and illustrated in the accompanying drawing wherein:

Figure 1 is a schematic view showing the relation of the control pumpsto the hoisting device, derrick and associated drilling equipment.

Figure 2 is a diagrammatic view Particularly in cross-section of thecontrol device of the present invention.

Figure 3 is a view in cross-section taken along the line 33 of Figure 2.

In Figure 1, a derrick I is provided with a crown block 2, a cable 3,with its dead end So and working end 3b, and a traveling block 4, fromwhich a swivel 5 and kell and drilling string 6 are suspended by meansof a hook 4a. The installation is devised for use in rotary drilling;however, the rotary table and other parts for rotating the drill string,as well as the portion of a,see,eia

drill string extending underground having a drill bit attached thereto,are not shown, being conventional. The working end of the cable 2biswound around a hoisting drum 1, which, by means oi. any suitable powertransmission device such as a drive belt or chain I, is coupled to adisplacement pump 0. which is the brake pump and may be or any suitabletype. If desired, a speed-multiplying transmission may be interposedbetween the d rum 1 and pump 0.

As the drill string lowered-into the borehole during drillingoperations, the weight of the drill string, insoiar as it is not takenup by the pressure of the bit on the bottom of the hole (weight on thebit). tends to rotate the drum 1 and the displacement pump 2.Consequently, the discharge pressure oi'the pump is proportional to thesuspended weight of the drilling string, trie tional resistances of thesystem being neglected. with the delivery side of the pump 2 closed, thehoisting drum I is unable to rotate ii. there is no leakage from thispump, which leakage, however, practically always occurs to a certainextent. In order to compensate for the pump leakage at all times, anindependently driven auxiliary pump II is provided, the constant outputof which is of suillcient volume to compensate for the leakage.

The auxiliary pump ll may be driven by any suitable motor Illa. Thedischarge pressure side l2 of the auxiliary pump II is connected to thedischarge pressure side I! of the pump 9 through a control device II,the operation of which is described with reference to Figure 2. Thisdevice I i isdesigned. apart trom maintaining the pump pressure at apredetermined and adjustable value, for periodically reducing the brakepump pressure for a short period.

Figure 2 shows the control device H as a unit together with the brakepump I and its delivery or discharge conduit 12, as well as theauxiliary pump I0 and its delivery conduit 12. The liquid beingdischarged from the control device it, said liquid being no longer underpressure, is returned to both pumps 9 and il in parallel through conduitH, in which a cooler 3 may be located. Any suitable liquid may beemployed in this system, such as an oil. forexample. For the purpose ofcontrolling the delivery pressure of both. pumps I and III, the controldevice ii is provided with a regulating slide valve 15, the bottom ofwhich is exposed to the discharge pressure of both pumps 2 and I0through conduits l2 and 13. The top of valve I5 is subjected to thepressure of a spring it, which urges the slide-valve downwards, and alsoto the pressure of a liquid of a lower pressure from conduit 29hereinafter referred to as regulating pressure. The position of theregulating slide valve i5 determines the size .of the opening of a port36, through which oil from the delivery pipes can escape to the outletl4, and, consequently, the magnitude of the delivery pressure from bothpumps 9 and 10.

Assuming a constant spring pressure, the delivery pressure of pumps 9and ll is determined by the regulating pressure prevailing on the top ofthe regulating slide-valve l5, which throttles the outlet passage 36.This regulating pressure is, in turn, controlled by means of theslidable piston valve l1 by means of which the space 21 above theregulating valve l5 may be put into comunicatlon through conduit 28,either with the space It, which is under delivery pressure fromauxiliary pump 10, or with the space i9, which is at the pump intake ornearly zero pressure. with the piston valve l1 in the central .duit 28and the outlet pipe M.

position (as shown) no communication is eifett ed with either space.

The piston valve 11 forms an integral part with the piston 20 and thepiston rod 2| extending upwards. By means of a ball-bearing gland 22 anda lever 22, this compound part or linkage, made up of elements 11-20-21,is subjected to a downward force. which is supplied by variable weights24 and an adjustable spring 25. When the piston 20 is in a position ofequilibrium, this downward force balances the upward force exerted bythe delivery pressure in space ll so that this delivery pressure can beadjusted by varying the weights 24 and the tension of the spring 2!. It,for some reason, the combined delivery pressure from pumps 0 and. itbecomes temporarily higher than the force applied by the lever 23, thepiston 20 and the piston valve 11 rise, the space 31 above theregulating valve II is brought into communication with conduits 2! and28, space ll, con- The pressure in space 31 will, therefore, decrease.Due to the decrease in pressure in space 21, theregulating valve itrises, the outlet port 28 opens and the delivery pressure from pump l0decreases until the piston 20 is once more in a state of equilibrium. Inthe case of a decrease in the delivery pressure, the opposite sequenceoi operations takes place in the control device II. p

In order to reduce the resistance 01' the piston 20 to movement in anaxial direction as much as possible. piston 20 is preferably rotated inany suitable manner, e. g., by means of the hydraulic motor 28, which isdriven by the liquid from the auxiliary pump Id. The rotatable pistonrod 21 is connected bysuitable linkage members l0 and H to cylindricalrotary slide valve 21. The linkage comprises an arm 4|] having one endfixedly secured to the piston rod 2|. The

other end of the arm 40 is fitted in a vertical slot H in the inner wallof the rotary valve 21. Thus. as arm it rises and falls with piston rod21. it will slide up or down in the slot ll without being disengagedtherefrom.

The rotary slide valve 21 is rotated together with the piston 20 by themotor 28, the rotary slide valve 21 being provided with an orifice ororifices 28, which momentarily register with one end of conduit 29,connected to the liquid-filled space 31 above the regulating valve l5.When, during the rotation of valve 21, the orifice 28 registers withconduit 2!, a small quantity of the liquid escapes through the port 42and the passage 43 in the piston 20 and the valve l1, thence throughchamber is and conduit 29 in the outlet pipe 14. This results in theregulating valve l5 rising a, short distance and the pressure under thisvalve decreasing slightly, owing to the enlargement of the outlet port36. Thus, the pump 9, it it is not in operation at that moment, developsa, tendency to start up. enabling it to overcome the static frictionalresistances in the system comprising the pump, the drilling tools andintermediate parts. As soon as conduit 29 is opened, it is closed againby the rotary slide valve 21 and the downward displacement of the piston20 and the piston valve l1 caused by the decrease in delivery pressurefrom pump l0, results in a flow of oil to the'space 31 above theregulating valve l5. until the original condition has been restored.

In this manner, the control device produces short impulses which are ofsuflicient magnitude to overcome, on the one hand, any staticresistances in the feeding system, but, on the other hand, have noeii'ect on the nominal bit pressure to be maintained. The quantity ofliquid leakink away each time through conduit 29 can be regulated bymeans 0! a normally open regulating valve 30, while the number ofimpulses per unit or time can be regulated by varying the number ofrevolutions of the hydraulic motor 26, e. g., by means of a by-pass withregulating valve 45. Instead of having only one opening 28, the rotaryslide valve 26 may be designed with a number of openings. In addition, anormally open valve 3! is incorporated in the conduit leading from thebrake pump 9, while parallel to this conduit there may be provided aby-pass with a nonreturn valve 32. with valve 2| in the closed position,it is possible to use the pump 9 as a motor by utilizing the liquidsupplied by pump l0 and so withdraw the drilling tools from the well.Use can also be made of valve 3| when the control device requiresadjustment.

The invention claimed is:

1. A speed-control system for a cable drum driven by the weight 01 adrill string supported thereby, said control system comprising a firstpump driven by the rotation of said drum, a second pump, a prime movertor the second pump, a closed fluid circuit, the high pressure side ofsaid circuit being connected to the exhaust sides of said pumps inparallel and the low. pressure side of said circuit being connected tothe intake sides of said pumps in parallel, variable orifice valve meansconnected in said circuit between the high and the low sides thereof tomaintain a back pressure on the first pump opposing the weightresponsive rotation of said drum, weighted pilot valve means responsiveto increases and decreases of pressure on the high side of said circuitfor increasing and decreasing the orifice of said first valve means, andmeans continuously actuating said pilot valve for periodicallyincreasing said orifice by small amounts.

2. A speed-control system for a cable drum driven by the weight of adrill string supported thereby, said control system comprising a firstpump driven by the rotation of said drum, a second pump, a prime moverfor the second pump, a closed fluid circuit, the high pressure side ofsaid circuit being connected to the exhaust sides of said pumps inparallel and the low pressure side of said circuit being connected tothe intake sides of said pumps in parallel, pressure-fluid actuatedvariable-orifice valve means connected in said circuit between the highand the low sides thereof to maintain a back pressure on the first pumpopposing the weight responsive rotation of said drum, weighted pilotvalve means responsive to increases and decreases of pressure on thehigh side of said circuit for increasing and decreasing the fluidpressure actuating said first valve means, third valve means forperiodically reducing-the fluid pressure actuating said first valvemeans whereby said orifice is increased by small amounts, and primemover means continuously actuating said third valve means to effect saidperiodical pressure reductions.

3. A speed-control system for a cable drum driven by the weight of adrill string supported thereby, said control system comprising a firstpump driven by the rotation of said drum, a second pump, a prime moverfor the second pump, a closed fiuid circuit, the high pressure side 0!said circuit being connected to the exhaust sides of said pumps inparallel and the low pressure side of said circuit being connected tothe intake sides of said pumps in parallel, pressure-fluid operatedvariable-orifice valve means connectedinsaidcircuit'between the high andthe low sides thereof to maintain a back pressure on the first. pumpopposing the weight responsive rotation. of said drum. first conduitmeans forming part of said circuit between the discharge of said secondpump and said variable-orifice valve for supplying an operating pressurefluid thereto, second conduit means forming part of said circuit betweensaid variable-orifice valve and the low pressure side of said circuitfor discharging operating pressure fluid from said valve, weighted pilotvalve means responsive to increases and decreases of pressure on thehigh side of said circuit for controlling the flow of pressure fluidthrough said first and second conduit means to and from said first valvemeans, third valve means in said second conduit means for periodicallyreducing the pressure fluid to said first valve, fluid motor means forcontinuously opening and closing said third valve means, and thirdconduit means between said motor means and said second pump to provide apressure fluid for operating said motor means.

4. A control system for well-drilling apparatus comprising a rotatabledrum, a cable suspending a drill string wound around said dium. wherebysaid drum is rotatably driven by said string, said control systemcomprising a first pump driven by the rotation of said drum, a secondpump, prime mover means for driving said second pump, intake anddischarge ports on said pumps, a pressure fluid control device, conduitmeans in communication between said control device and the intake anddischarge ports of said pumps forming a closed fluid circuit betweensaid pumps and said control device, said second pump being adapted tofurnish a supply of pressure fluid for operating said control device andcompensating for leakage from said first pump, said pressure fluidcontrol device comprising first valve means in said fluid circuitadapted to throttle the fluid flow therein, thereby maintaining a backpressure on said first pump to oppose the unwinding of said cable fromsaid drum, pilot valve controlling means for the setting of said firstvalve. means for biasing the pilot valve to maintain the back pressureat a predetermined value, fluid conduit means in communication betweensaid first and second valve means andthird valve means in said conduitmeans for periodically reducing said back pressure by a small amount.

5. A control system for well-drilling apparatus comprising a rotatabledrum, a cable suspending a drill string wound around said drum, wherebysaid drum is rotatably driven by said string, said control systemcomprising a first pump driven by the rotation of said drum, a secondpump, prime mover means for driving said'second pump, intake anddischarge ports on said pumps, a pressure fluid control device, conduitmeans in communication between said control device and the intake anddischarge ports of said pumps forming a closed fiuid circuit betweensaid pumps and said control device, said second pump being adapted tofurnish a supply of pressure fluid for operating said control device andcompensating for leakage from said first pump, said pressure fluidcontrol device comprising fluid-operated first valve means in said fiuidcircuit adapted to throttle the fluid flow from said pumps, therebymaintaining a back pressure on said first pump to oppose the unwindingof said cable from said drum, first conduit means forming part of saidcircuit in communication between the discharge port of said second pumpand the low pressure side of said first valve means, second conduitmeans forming part of said circuit in communication between thedischarge port from the control device and the low pressure side of thefirst valve means, second valve means in said first and second conduitmeans for controlling the flow to and from the low pressure side of saidfirst valve means, spring means in said first valve means acting againstthe low pressure side thereof means biasing the second valve means tomaintain the back pressure at a predetermined value, and third valvmeans in said second conduit means for periodically reducing said backsmall amount.

pressure by a ALFONS a. H. STRAATMAN REFERENCES CITED The followingreferences are of record in the file of this patent:

UNITED STATES PATENTS 10 Number

